Enter your battery's voltage (V) and charge in mAh or Ah to calculate watt-hours (Wh) — the true measure of stored energy. You can also calculate Wh from power (watts) and time (hours) directly. Switch between mAh → Wh and Wh → mAh conversion modes to get the result you need.
Watt-hours (Wh)
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Kilowatt-hours (kWh)
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Milliamp-hours (mAh)
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Energy in Joules (J)
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Use the formula: Wh = (mAh × V) / 1000. For example, a 10,000 mAh battery at 3.7V stores 37 Wh of energy. Simply multiply the milliamp-hours by the voltage and divide by 1,000.
The converter multiplies your battery's charge in milliamp-hours (mAh) by its voltage (V) and divides by 1,000 to give watt-hours. This works because power (watts) = current (amps) × voltage, and 1 mAh = 0.001 Ah.
Watt-hours give a more accurate measure of usable energy because they account for both charge and voltage. Two batteries with the same mAh but different voltages store different amounts of energy. Wh lets you compare them fairly — and is the unit used by airlines for carry-on limits.
Multiply the device's power rating in watts by the number of hours it runs: Wh = W × h. For example, a 60W light bulb running for 5 hours uses 300 Wh (0.3 kWh) of energy.
Rearrange the formula: mAh = (Wh × 1000) / V. For example, a 37 Wh battery at 3.7V equals 10,000 mAh. You need to know the voltage to make this conversion.
It depends on the voltage. At 12V: Ah = 500 / 12 ≈ 41.7 Ah. At 3.7V: Ah = 500 / 3.7 ≈ 135.1 Ah. Always divide watt-hours by the battery's voltage to get amp-hours.
One watt-hour is the amount of energy consumed or stored when 1 watt of power flows for 1 hour. It equals 3,600 joules. A typical smartphone battery holds around 10–15 Wh, while a laptop battery holds 40–100 Wh.
Most lithium-ion cells (like those in smartphones and power banks) operate at a nominal voltage of 3.7V. USB-powered devices typically use 5V, car batteries use 12V, and AA alkaline batteries use 1.5V. Check your device label for the exact value.